When Jack (Jeremy Northam) wraps his handkerchief around Angela's (Sandra Bullock's) bare midriff, it borrows directly from the Alfred Hitchcock thriller Notorious (1946), wherein Cary Grant does the same thing to Ingrid Bergman, cautioning her that without it, she might catch cold.
On the checklist on Angela's computer, it says "Bring 2600 Mag," and 2600 is a real hacker's magazine.
The game that Angela is playing/debugging at the beginning of the movie is the Apple version of Wolfenstein 3D (1992), similar to the console editions of the game released on the Atari Jaguar and 3DO.
One of the few PG-13 rated movies permitted to use the word "fuck" in a sexual context.
In the park where where Bergstrom ends his life, the sculpture of the half-buried giant is "The Awakening" by Seward Johnson. It was relocated from Hains Point to National Harbor in 2008.